1. Technical Field
The present disclosure relates to an ultrasonic cutting device and method for sensing, measuring, and adjusting tissue properties. More particularly, the present disclosure relates to an ultrasonic cautery cutting device including a feedback mechanism for automatically adjusting, in real-time, ultrasonic waves applied to tissue.
2. Background of the Related Art
Ultrasonic instruments are effectively used in the treatment of many medical conditions, such as removal of tissue and cauterization of vessels. Cutting instruments that utilize ultrasonic waves generate vibrations with an ultrasonic transducer along a longitudinal axis of a cutting blade. By placing a resonant wave along the length of the blade, high-speed longitudinal mechanical movement is produced at the end of the blade. These instruments are advantageous because the mechanical vibrations transmitted to the end of the blade are very effective at cutting organic tissue and, simultaneously, coagulate the tissue using the heat energy produced by the ultrasonic frequencies. Such instruments are particularly well suited for use in minimally invasive procedures, such as endoscopic or laparoscopic procedures, where the blade is passed through a trocar to reach the surgical site.
For each kind of cutting blade (e.g., length, material, size), there are one or more (periodic) driving signals that produce a resonance along the length of the blade. Resonance results in optimal movement of the blade tip and, therefore, optimal performance during surgical procedures. However, producing an effective cutting-blade driving signal is not a trivial task. For instance, the frequency, current, and voltage applied to the cutting tool must all be controlled dynamically, as these parameters change with the varying load placed on the blade and with temperature differentials that result from use of the tool.
FIG. 1 shows a block schematic diagram of a prior-art circuit used for applying ultrasonic mechanical movements to an end effector. The circuit includes a power source 102, a control circuit 104, a drive circuit 106, a matching circuit 108, a transducer 110, and also includes a handpiece 112, and a waveguide 114 secured to the handpiece 112 (diagrammatically illustrated by a dashed line) and supported by a cannula 120. The waveguide 114 terminates to a blade 116 at a distal end. A clamping mechanism referred to as an “end effector” 118, exposes and enables the blade portion 116 of the waveguide 114 to make contact with tissue and other substances.
The drive circuit 106 produces a high-voltage self-oscillating signal. The high-voltage output of the drive circuit 106 is fed to the matching circuit 108, which contains signal-smoothing components that, in turn, produce a driving signal (wave) that is fed to the transducer 110. The oscillating input to the transducer 110 causes the mechanical portion of the transducer 110 to move back and forth at a magnitude and frequency that sets up a resonance along the waveguide 114. For optimal resonance and longevity of the resonating instrument and its components, the driving signal applied to the transducer 110 should be as smooth a sine wave as may practically be achieved. For this reason, the matching circuit 108, the transducer 110, and the waveguide 114 are selected to work in conjunction with one another and are all frequency sensitive with and to each other.
Because a relatively high-voltage (e.g., 100 V or more) is required to drive a typical piezoelectric transducer 110, the power source that is available and is used in prior-art ultrasonic cutting devices is an electric mains (e.g., a wall outlet) of, typically, up to 15 A, 120 VAC. Therefore, most ultrasonic cutting devices resemble that shown in FIGS. 1 and 2 and utilize a countertop box 202 with an electrical cord 204 to be plugged into the electric mains 206 for supply of power. Resonance is maintained by a phase locked loop (PLL), which creates a closed loop between the output of the matching circuit 108 and the drive circuit 106. For this reason, in prior art devices, the countertop box 202 includes all of the drive and control electronics 104, 106 and the matching circuit(s) 108. A supply cord 208 delivers a sinusoidal waveform from the box 202 to the transducer 110 within the handpiece 112 and, thereby, to the waveguide 114.
A disadvantage exists in the prior art due to the frequency sensitivity of the matching circuit 108, the transducer 110, and the waveguide 114. By having a phase-locked-loop feedback circuit between the output of the matching circuit 108 and the drive circuit 104, the matching circuit 108 is required to be located in the box 202, near the drive circuit 108, and separated from the transducer 110 by the length of the supply cord 208. This architecture introduces transmission losses and electrical parasitics, which are common products of ultrasonic-frequency transmissions.
In addition, prior-art devices attempt to maintain resonance at varying waveguide 114 load conditions by monitoring and maintaining a constant current applied to the transducer. However, the only predictable relationship between current applied to the transducer 110 and amplitude is at resonance. Therefore, with constant current, the amplitude of the wave along the waveguide 114 is not constant across all frequencies. When prior art devices are under load, therefore, operation of the waveguide 114 is not guaranteed to be at resonance and, because only the current is being monitored and held constant, the amount of movement on the waveguide 114 may vary greatly. For this reason, maintaining constant current is not an effective way of maintaining a constant movement of the waveguide 114.
Furthermore, in the prior art, handpieces 112 and transducers 110 are replaced after a finite number of uses, but the box 202, which is vastly more expensive than the handpiece 112, is not replaced. As such, introduction of new, replacement handpieces 112 and transducers 110 frequently causes a mismatch between the frequency-sensitive components (108, 110, and 112), thereby disadvantageously altering the frequency introduced to the waveguide 114 and the energy applied to tissue. One way to avoid such mismatches is for the prior-art circuits to restrict themselves to precise frequencies. This precision brings with it a significant increase in cost.